Articles such as glasses for vehicles and buildings which are transparent and exposed to sunlight for a long period of time for their uses have been generally coated with colored films or vacuum-deposited with metals on their surfaces in order to shield a part or light. However, since theses methods always shield visible ray at a predetermined ratio regardless of the light intensity, there are problems in that the field of view becomes dark at night or on a cloudy day.
There are several articles named photochromic films, but most of them are extrusion-molded films prepared by master-batching resins such as polyethylene, polypropylene, polystyrene, and ABS. Since these films do not have a good transparency, they are generally used as agricultural films which do not require transparency, and impracticable as photochromic films for vehicles requiring a wide field of view.
Korean Patent Publication No. 2003-0089544 discloses a photochromic film prepared by coating a basic polyester (PET) film with a photochromic acrylic-based adhesive to a suitable thickness, which is intended to use as a vehicle tinted film. However, this photochromic film does not have good durability, and thus it is easily damaged.
On the other hand, to improve the performance of photochromic films, various solid additives such as a dye, an initiator, a UV stabilizer, and an antioxidant are added to a binder resin to produce photochromic films. Therefor, it is important that these solid additives have to be well dispersed in the binder resin. When the photochromic film is produced by a solvent-free cell casting method, a pore size of the film matrix can be suitably controlled, and a photochromic film having high durability can be produced, as compared to a method using the polymer itself dissolved in a solvent as a material for the production of the film. However, there is a problem in that the aforementioned solid additives are not dissolved well in the known photochromic composition which is employed in the solvent-free cell casting method. For example, when typical dyes other than photochromic dyes are used for initial color adjustment of the photochromic film, it is difficult to develop a desirable color due to their low solubility to the known photochromic film binder. In addition, in a combination of the known acrylate monomers for the production of the photochromic film, they are problematically filtered out or precipitated due to the low solubility of the typical dyes and UV stabilizer.